Adhesive materials, including pressure sensitive adhesives (PSAs), are commercially available for use in any of a variety of applications and industries such as in the construction of mounting tapes, carpet tapes and the like. Some carpet tapes comprise a backing, such as, for example, a cloth or film backing, with an adhesive coating on each of the major surfaces of the backing. Adhesives used in carpet tape applications have typically been pressure sensitive adhesives having (1) aggressive and permanent tack, (2) adherence to both a substrate and an adherend (e.g., a carpet backing) with no more than finger pressure, and preferably (3) being removable from the adherend. Pressure-sensitive adhesive tapes, such as carpet tapes, provide a strong bond to substrates because separation of the tapes from the substrates is neither intended, nor desired. When removal of the carpet is desired, pressure sensitive carpet tapes made with aggressively tacky PSAs have been very difficult to remove from a substrate and may result in damage to the substrate or may leave a tacky adhesive residue. Substrate damage is especially problematic for aerospace carpet tape applications where the substrate, e.g., a floor panel, may be costly to replace. Moreover, during the life of a carpet, dirt is ground into the carpet fabric and, over time, penetrates through the carpet to damage the underlying tape by causing nicks, cuts or small tears in the tape backing. When the carpet is subsequently removed, the damage to the backing can cause the tape to break, making it more difficult to remove from the substrate.
Some pressure sensitive adhesives have been specifically formulated to allow clean and easy removal from substrates after use, such as, for example, the adhesive used for Post-It® brand removable notes, available from Minnesota Mining and Manufacturing Company of St. Paul, Minn. These adhesives, however, do not possess sufficient tack to provide a level of holding power sufficient for use in carpeting applications, for example. In general, adhesives that are formulated to provide a substantial level of adhesion, e.g., for holding a carpet to a substrate, are difficult to remove from a substrate without significant effort.
U.S. Pat. No. 4,024,312 discloses a film backed, normally tacky and pressure-sensitive adhesive tape which is highly extensible and highly elastic. The tape can be removed from a surface to which it has been applied by stretching it lengthwise in a direction substantially parallel to the plane of the surface. The film backing is formed from a composition comprising elastomeric and thermoplastic A-B-A block copolymers and possesses a lengthwise elongation to break of at least about 200%, and a 50% rubber modulus of not above about 2,000 lbs/sq. inch. This low rubber modulus is stated to be an important factor in insuring easy stretchability and easy removal of the tape at high elongations. The elasticity of the backing is important for conformability and other purposes, and the elastic recovery from 50% stretch is stated as at least about 75%, more preferably at least about 90%.
German (OS) 3331 016 A1 discloses another adhesive tape for removable adhesive bonds, whereby the tape exhibits high elasticity and low plasticity. The adhesive strength is less than the cohesive strength, and the adhesion capability essentially disappears as the film is being stretched. The ratio of peel force to tear strength of the tape is about 1:2 or greater, and the adhesive bond can be released by pulling the film in the direction of the plane of the adhesive joint. The tape is used as a load-resistant adhesive to bond two rigid solid substrates. A separation of the adhesively bonded materials is possible without damage to the substrate.
The pressure sensitive adhesives described in U.S. patent application Ser. No. 09/764,478 now abandoned comprise a fibrous reinforcing material. The patent application describes the fibrous reinforcement of pressure sensitive adhesives to provide “stretch removable” characteristics. The fiber reinforced adhesive composition comprises a pressure sensitive adhesive matrix with a fibrous reinforcing material therewithin. The fiber reinforced adhesive composition is described as providing improved cohesive strength over the pressure sensitive adhesive alone, while the tack of the pressure sensitive adhesive remains substantially unreduced by the presence of the fibers.
In applications for tapes and other articles, a fire retardant feature may be needed and, in certain applications, may be required by applicable regulations. For example, tapes for electric or electronic applications may be directly exposed to electrical current, to short circuits, and/or to heat generated from the use of the associated electronic component or electrical device. Consequently, industry standards or regulations may impose conditions on the use of such tape articles that require qualifying tests be performed on the tapes such as burn tests, and the like. For electrical and electronics applications, the industry standard flammability test is Underwriters Laboratories (UL 94 “Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances”). For rail transit applications, the industry standard is American Society for Testing and Materials ASTM E662 (“Test Method for Specific Optical Density of Smoke Generated by Solid Materials”) and ASTM E162 (“Test for Surface Flammability of Materials Using a Radiant Energy Source”).
For aerospace applications, the testing criteria for the Federal Aviation Administration F.A.R. § 25.853 (July 1990) vertical burn test, subparagraph (a)(1)(i), relates to interior compartments occupied by crews or passengers, including interior ceiling panels, interior wall panels, partitions, galley structures, large cabinet walls, structural flooring, and materials used in the construction of stowage compartments. F.A.R. § 25.853 (July 1990) subparagraph (a)(1)(ii) relates to carpet tapes, seat cushions, padding, decorative and non-decorative coated fabrics, leather, trays and galley furnishings, electrical conduit, thermal and acoustical insulation and insulation covering air ducting, joint and edge covering and the like. Materials used for these applications must be self-extinguishing when tested vertically in accordance with the procedures of F.A.R. § 25.853 (July 1990) (a)(1)(i) and (a)(1)(ii). In addition for both rail transit and aerospace applications, another industry standard is Boeing Specification Support Standard, BSS 7239 (“Test Method for Toxic Gas Generation by Materials of Combustion”) which requires analysis of combustion gases and has specified concentration limits on toxic gases which currently include HCN, NOx, CO, HCl, HF, and SO2.
In particular, carpet tapes for aerospace applications are presently defined by the Boeing Material Specification BMS 5-133C and are classified according to the following:                Type II, Class 1—Maximum weight 16 oz/yd2, white color;        Type II, Class 2—Maximum weight 16 oz/yd2, black color;        Type III—Maximum weight 24 oz/yd2, white color;        Type IV, Class 1—Differential tack, maximum weight 5.0 oz/yd2, black color on side 2; and        Type IV, Class 2—Differential tack, maximum weight 9.0 oz/yd2, black color on side 2.This specification lists key tests and requirements for each of the different Types. The specification includes weight, flammability according to F.A.R. § 25.853 (July 1990) (a)(1)(i) (12 Second Vertical Burn), tensile strength, peel strength, lap shear strength, corrosion to aluminum, and release liners.        
In order to meet the requirements imposed on them in such applications, tapes and other articles may be made with materials that are naturally resistant to fire as well as materials that have been processed or manufactured to impart a fire retarding or fire resistant quality by incorporating fire retardant agents and the like. Current carpet tapes for aerospace applications utilize the fire retardants antimony trioxide and polybrominated biphenyls, specifically, decabromodiphenylether (deca-BDE). However, European authorities have recommended a ban of some of the polybrominated biphenyls as soon as Jul. 1, 2003. Such a ban will necessitate redesigned, reformulated tapes. Also in Europe, the Waste from Electrical and Electronic Equipment directive has proposed that halogenated flame retardants and certain other materials be phased out by January 2004.
Two key features are driving the need for an improved fire retardant carpet tape invention for aerospace industry.                1. Environment regulations requiring acceptable fire retardant systems; and        2. Clean removable tapes which effectively and efficiently improve the removal process and eliminate damage to floor substrates and which do not leave adhesive residue.        
Cleanly removable tapes would provide a cost saving to the aerospace industry and would reduce or eliminate the need to use solvents to remove adhesive residues. Fire retardant carpet tapes will eventually be required to meet the new environmental legislation being adopted in Europe and around the world.
It would be desirable to provide pressure sensitive adhesive tapes and methods for the manufacture of such tapes. More specifically, it would be desirable to provide pressure sensitive adhesive tapes in the form of multi-layer tapes, such as, double-sided tapes, and the like that can be easily cleanly removed from a substrate without leaving significant adhesive residue. It would be especially desirable to provide these pressure sensitive adhesive tapes in a form that permits their removal from a substrate using a stretch-release mechanism, and wherein the tapes are fire retardant and satisfy government and/or industry flammability regulations.